1. Field of the Invention
The present invention relates to a dead weight display apparatus for displaying weight loaded on a vehicle, more particularly on a bed of a vehicle for carrying cargo so as to prevent an overload.
2. Description of the Related Art
A dead weight display apparatus of the foregoing type has been structured such that loads applied to the front and rear wheels of the vehicle are detected by sensors and weight is calculated in accordance with signals output from the sensors so as to issue an alarm if the dead weight becomes excessive. However, since loads applied to the sensors are changed during running of the vehicle, an accurate dead weight cannot be displayed. Accordingly, there has been suggested a structure capable of preventing the foregoing problem in Japanese Patent Unexamined Publication No. Hei. 8-50054.
The dead weight display apparatus suggested as described above has a structure such that the weight calculated in accordance with output signals from sensors is not displayed on a display unit as it is during running of the vehicle. As an alternative to this, the weight detected before start of running by a predetermined time is displayed and display of this weight is retained until another predetermined time elapses after running has been stopped. That is, the weight detected before start of running by a predetermined time is displayed in a period from start of running of the vehicle to a moment at which a predetermined time has passed from stoppage of the vehicle. If start of a loading/unloading operation has been detected after a predetermined time has elapsed from stoppage of the vehicle, the weight calculated in accordance with output signals from the sensors can be correspondently displayed on the display unit. The weight detected after the vehicle has been stopped does not always coincide with the weight detected before start of running of the vehicle even if loading or unloading is not performed. Therefore, the difference between weights calculated sequentially is added to the weight displayed previously so as to update the display after the vehicle has been stopped.
Incidentally, since a vehicle on which the dead weight display apparatus is mounted has a car body A of the vehicle which is, as shown in FIG. 14(a), supported by front and rear wheels, the central portion of a buffer member D made of a leaf spring is secured to an axle portion C of each wheel B. Moreover, the two longitudinal ends are rotatively connected to two portions in the bottom of the car body by support shafts E1 and E2. Sensors S for detecting loads respectively added to the front and rear wheels of the vehicle are usually accommodated and attached in the support shafts for rotatively connecting one of the two longitudinal ends of the buffer member to the bottom portion of the car body as shown in FIG. 14(a). The sensors for the front wheels are attached to the rear support shaft E2 and those for the rear wheels are attached to the front support shaft E1.
In the above-mentioned structure, weights of the car body A and the cargo are shared and added to the respective wheels. For example, the front wheel bears reaction force F having the magnitude corresponding to that of a load added to the wheel B from the portion adjacent to the ground, as shown in FIG. 14(a). The reaction force F is shared by the support shafts E1 and E2 at the two longitudinal ends of the buffer member D. When a driver applies the foot to the brake pedal to stop the running vehicle and the vehicle is thus stopped in a state where the foot is applied to the brake pedal, a state is realized in which force F2 borne by the rear support shaft E2 of the buffer member D is made to be larger than force F1 borne by the front support shaft E1 of the same.
If the above-mentioned state is realized, the sensor S accommodated in the rear support shaft E2 detects weight heavier than the weight which must be detected. However, the foregoing fact does not raise a problem in a state where the brake is not released, that is, the brake is operated.
If the brake is released or moderated after the vehicle has been stopped, the deviated force is released so that force F1' borne by the front support shaft E1 at one of the two ends of the buffer member D and force F2' borne by the rear support shaft E2 are gradually changed so as to be substantially equal to each other, as shown in FIG. 14(b). Therefore, the weight which is detected by the sensor S accommodated in the rear support shaft E2 is gradually changed from heavy weight detected before the brake is released to light weight.
Therefore, if the brake is released or moderated before a predetermined time elapses from stoppage of the vehicle, the weight which is detected by the sensor S is changed instably. If an operation for detecting start of a loading/unloading operation is performed in the above-mentioned period, weights sequentially calculated in accordance with output signals from the sensors which are changed even if no loading/unloading operation is performed becomes different. The difference in weight is added to the previously displayed weight to update the display. Therefore, even if a loading/unloading operation is not actually performed, display as if the weight has been reduced is performed on the display unit.
The weight displayed on the display unit is used as a reference value of the weight which is enlarged or reduced attributable to the afterward loading/unloading operation. If the weight is enlarged attributable to the afterward loading operation, smaller weight is displayed. According to circumstances, display does not reflect an overload. The overload state cannot be determined and thus an alarm cannot be issued.